JPS63263629A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the dispersibility of magnetic powder into a binder and to obtain a recording medium having excellent running durability by specifying the mol.wt. of a high-molecular polymer to be used for the binder. CONSTITUTION:The binder is selected from a group of a vinyl chloride system and urethane resin and the weight average mol.wt. thereof is specified to 20,000-80,000. The content of the binder having <=3,000mol.wt. is confined to <=3wt.%. powder of a magnetic alloy having >=40m<2>/g specific surface area is used for a ferromagnetic material. Particularly -SO2M, -OSO3M, -COOM, -OPO(OM1)(OM2), -PO(OM1)(OM2) are incorporated at 1-50X10<-6>equiv./g into the binder and further, a polyisocyanate compd. is incorporated therein. M, M1, M2 is respective substituents are H, alkali metal atoms or -NR1R2R3R4 (where R1-R4 are H, alkyl group of 1-12C, alkenyl group, substd. alkyl group or substd. alkenyl group). The durability and surface characteristic in particular are improved if the magnetic recording medium is produced by using the binder constituted in such a manner.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium, and particularly to a magnetic recording medium containing fine ferromagnetic powder with improved durability and surface properties.

The magnetic recording medium according to the present invention is used as a "magnetic tape, a 1w1 sheet" or a 1magnetic disk 8.

[Prior art and its problems]

With the rapid development in the field of magnetic recording technology, the performance of magnetic recording media is increasingly required to be improved, and in particular, magnetic recording media for video are required to have high playback output for short wavelength recording. Therefore, efforts are being made to meet these demands by making the ferromagnetic powder that is normally used in the magnetic layer of magnetic recording media highly fine-grained, or by proposing new compositions for the binder.

However, even if the binder compositions proposed for conventional magnetic layers are improved in certain respects, other defects may occur.
At present, a binder composition with perfect performance has not yet been achieved.

Conventionally, binders for this magnetic layer include vinyl chloride vinyl acetate copolymer, cellulose resin, polyurethane resin, acrylic resin, vinylidene chloride resin, epoxy resin, phenoxy resin, synthetic rubber resin, and polyester resin. A large number of synthetic resins are used alone or in combination of two or more. In particular, compositions consisting of a combination of a polyurethane resin and a vinyl chloride vinyl acetate copolymer or a combination of a polyurethane resin and a cellulose resin have been considered preferable.

In particular, recently, in order to meet the above-mentioned requirements, ferromagnetic powder has been made into highly fine particles, ferromagnetic powder with even higher coercive force is used, and the surface of the resulting magnetic layer has been smoothed to achieve a high S/N. They tend to try to get what they want. However, when the ferromagnetic powder in the magnetic layer is made into fine particles,
Due to the fine particle nature and magnetism of the powder, the powder particles are strongly bonded and aggregated, making it extremely difficult to uniformly disperse them in the binder. If the ferromagnetic powder is not sufficiently dispersed within the magnetic layer, the uniformity of the magnetic layer, the orientation of the powder itself in the magnetic layer, and the surface properties of the magnetic layer will be poor, resulting in a high S/N. It cannot be obtained. Furthermore, when the ferromagnetic powder is made into finer particles, its specific surface area increases, and the contact interface between the ferromagnetic powder and the binder solution increases, requiring more energy to disperse the ferromagnetic powder. do. This problem can be solved to some extent by improving the mixing and dispersing machine for the magnetic composition, but there are limits to this. Conventionally, therefore, a method of adding a surfactant having dispersion ability to a composition for magnetic formation has been adopted, but in order to improve the dispersion ability, increasing the amount of surfactant added results in a magnetic layer. A new problem arises in that the physical properties of the material deteriorate.

Furthermore, magnetic recording media have the problem of charging, and in order to suppress charging properties, carbon black or an antistatic agent is generally added to the composition for forming the magnetic layer.
This method sometimes causes problems with adhesive failure due to a drop in S/N and blooming. Recently, improvements have been made to the binder itself in order to improve the dispersibility of fine ferromagnetic powder in the binder and to provide antistatic properties. -〇〇〇X, -so, x, -osos x.

A binder having a polar group consisting of POsX*t or OPO* . This binder attracted attention as being able to achieve the above objectives to some extent, but
Sufficient characteristics regarding running durability cannot be obtained, especially 5IF
It has been found that when a fine ferromagnetic material with a T specific surface area of 40 po/g or more is used, running durability is significantly inferior and furthermore, running tension increases. In particular, the running performance is poor under harsh running conditions and high humidity conditions, and new technology to solve these problems is desired.

[Means and effects for solving the problems] The present invention solves the problems in the prior art described above, that is, it provides a magnetic layer of a magnetic recording medium with good dispersibility of ferromagnetic fine powder in a binder. The purpose of the present invention is to obtain a magnetic recording medium with excellent running durability, and as a result of intensive research on the molecular weight of the high molecular weight polymer used as a binder, the present inventors have identified these characteristics. The present inventors have discovered that the above object is achieved and the running durability of the magnetic recording medium is significantly improved in the case of the present invention.

That is, the present invention provides a magnetic recording medium in which a magnetic layer in which fine ferromagnetic powder is uniformly dispersed in a binder is provided on a nonmagnetic support, wherein the binder has a weight average molecular weight of 20,000. ~80,000, and has a weight average molecular i of 3,000 or less at 3% by weight or less, and is made of at least one member selected from the group consisting of vinyl chloride resins and urethane resins. A recording medium, particularly a magnetic recording medium in which the ferromagnetic material is a ferromagnetic alloy having a specific surface area (Sstt) of 40rd/g or more as measured by the BET method, and the binder is -3
Ox M, O20:l M, C00M, O
PO (OMI) (OMt), PO (OM +) (
OMt), [M, M+ and Ml in each of the above substituents are
Hydrogen atom, alkali metal atom or -NRr Rt R
5Ra (R+, Rt, Rs and R4 are hydrogen atoms, alkyl groups having 1 to 12 carbon atoms, alkenyl groups,
A magnetic recording medium containing 1 to 50 x 10-6 equivalents/g of ) representing a substituted alkyl group or a substituted alkenyl group, and further containing a polyisocyanate compound in addition to the binder. It is a medium.

The present invention will be explained in detail below.

The magnetic recording medium of the present invention basically has a magnetic layer in which a strong n-type fine powder is dispersed in a binder on a non-shadow support.

Examples of ferromagnetic materials include iron oxide-based ones and alloy-based ones.0 A specific example of ferromagnetic iron oxide is 7-FetOs.
, weakly reduced 1-Fe,O.

(mixed crystal of T Fezes and Y'ezOa), or Co-coated ferromagnetic iron oxide in which a Co compound is deposited on the surface of these ferromagnetic iron oxides. γ-Fe! 0. R-FetOs and weakly reduced r-FetOs can be produced by various methods, but generally, hydrous iron oxides such as goethite or lepidocrocite are used as starting materials and reduced to magnetite, and this magnetite is further processed. Ferromagnetic T- with acicular crystal type by oxidation
Fe, O, or weakly reduced T-Fe.

0, is generated. Co-coated ferromagnetic iron oxide is produced by suspending the r-FetOs particles obtained as described above in water, and adding a Co compound such as cobalt chloride and an excess of sodium hydroxide to this suspension. A Co compound is deposited on the surface of the T-Fezes particles by adding an alkali such as alkali, and the resulting particles are taken out from the reaction solution.
If necessary, it can be obtained by heat treatment at a relatively low temperature of, for example, about 120°C. These iron oxide particles have a specific surface area (
30 m2/g or more, preferably 40 m2/g
It is necessary that it is above. Smty is 3Om2/
This is because iron oxide particles of less than 1 g cannot be expected to have much of an effect on improving S/N. And this SIE?
Ferromagnetic particles of 30 rrf/g or more can be obtained by selecting the size of the starting material, hydrated iron oxide particles, or 5 m1t.

On the other hand, specific examples of ferromagnetic metals include Fe or Fe
and others such as Ti, v, Cr%Mn.

Co, Ni, Cu5ZnSS t, p, Mo, Sn.

There are alloys with metals such as Sb and Ag. These ferromagnetic metals can be prepared, for example, by thermally decomposing an organic acid salt of a ferromagnetic metal and reducing it by contacting it with a reducing gas, by using acicular oxyhydroxides or these containing other metals, or by using these methods. A method of reducing acicular iron oxide obtained by heating oxyhydroxide by contacting it with a reducing gas, a method of thermally decomposing a metal carbonyl compound, a method of evaporating a ferromagnetic metal in a low pressure inert gas, A method of reducing with a reducing substance such as a boron hydride compound, hypophosphite or hydrazine in an aqueous solution of a metal salt capable of forming a ferromagnetic substance;
It can be manufactured by a method in which ferromagnetic metal powder is electrodeposited using a mercury cathode and then separated from the mercury. The particles of the ferromagnetic metal powder thus obtained have a specific surface area (Smzt) of 40rrf as measured by the BET method.
/g or more, preferably 45rrf/g or more, and this ferromagnetic metal fine powder is one of the particularly preferred ones for the present invention. S07 is 45rrr/
This is because ferromagnetic metal particles with a particle size of less than 1 g cannot be expected to have much of an effect on improving the S/N ratio. And this S□t
Ferromagnetic particles larger than 45 rd/g can be obtained by selecting the particle size and 5ect in the starting material.

This ferromagnetic metal powder has a coercive force Hc of 1.000 when the purpose of the magnetic recording medium used is short wavelength recording.
The acicular ratio of the powder is preferably 7 or more in order to ensure the necessary coercive force Ha and to improve the orientation of the magnetic particles.

The most distinctive feature of the present invention is that the binder used to form the magnetic layer has a weight average molecular weight of 20,000 or more.
It is at least one selected from the group consisting of vinyl chloride resins and urethane resins, which has a weight average molecular weight of 3,000 or less and has a weight average molecular weight of 3,000 or less, and has a weight average molecular weight of 3,000 or less. 3Ox M, 03Oz
M, C00M, 0PO(OM +) (OM
g), -PO(OM,)(oMx) (M, Ml and M in each of the above substituents are a hydrogen atom, an alkali metal atom,
or -NRRz Rs Ra (Rt, R1, Rs and R4 represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group, a substituted alkyl group, or a substituted alkenyl group)] is 1 to 50 It contains 10-6 equivalent/g and further contains a polyisocyanate compound.

X in the polar group is -NR, R1R1R, and R, R1, R3, and R4 are hydrogen atoms, alkyl groups having 1 to 12 carbon atoms, alkenyl groups, substituted alkyl groups, or l! There are substituted alkenyl groups, but in these polar groups, Rt, Ri, R8 and R4 preferably have an average of 1 or less hydrogen atoms. Examples of alkyl groups include methyl, ethyl, propyl, butyl. Substituted alkyl groups include tolyl and methylol groups, and alkenyl groups include vinyl and propynyl groups. In the present invention, characteristic polar groups include, for example, -COO
, -S Os , -0S O3, P Os , -〇 P
-NH(CtIs)s with either Os etc.
, -NH(Ct Hs ) x C6R13,N (Ct
There are combinations such as Is) 4.

The above polar group-containing polymer is generally synthesized by the following reaction. That is, these polymers are -COOI(, -3o, H, -0Sow H, -PO
3Hz, or -0PO, H-rich groups, for example, the reaction of a vinyl chloride polymer or polyurethane resin with an alkylamine, dialkylamine, trialkylamine, tetraalkylammonium hydroxide, etc., or the above-mentioned reaction. copolymerization of a polymerizable unsaturated (double bond-containing) compound containing a polar group with another copolymerizable compound, condensation of a polyhydric alcohol containing the above polar group with a diisocyanate, the above polar group It is synthesized by condensation of dicarboxylic acid containing dicarboxylic acid and polyhydric alcohol. In addition to the above-mentioned polar groups, the actual polymer may also contain polar groups such as hydroxyl groups, epoxy groups, and isocyano groups.

The present invention is particularly characterized in that the polymer is a vinyl chloride resin and/or a polyurethane resin, and a method for introducing the above polar group into the vinyl chloride resin and/or polyurethane resin will be explained. .

■ Vinyl chloride resin with a polar group introduced A polar group is introduced into the side chain of a vinyl chloride resin, and has the following general formula: % formula %) [In the formula, X is the above polar group, Y represents a monomer having a vinyl group that can be copolymerized with vinyl chloride, and 1%
m and n each represent the degree of polymerization of each component. In the above general formula, each component of the polymer is shown as being arranged regularly in sequence for convenience, but in addition to the cases represented by the above general formula, each component is regularly repeated in a fixed proportion. They may be arranged or randomly arranged. These resins can be synthesized using conventional techniques.

In the above general formula, the vinyl chloride component is related to the strength of the magnetic layer film and the solubility in solvents, and its degree of polymerization l is 100.
If it is smaller, the desired strength cannot be obtained, and if it is larger than 1,000, the solubility in solvents will be poor. The vinyl component that has a polar group in
The polar group improves the dispersibility of the ferromagnetic fine powder in the magnetic layer, but the effect is insufficient if the degree of polymerization n is less than 0.1, and even if it is greater than 100, the dispersibility is improved. The degree of polymerization of the vinyl component having a polar group is preferably from 0.1 to 100, since it does not contribute much to moisture resistance and, on the contrary, causes problems in terms of moisture resistance.

In addition to the copolymerizable monomers mentioned above, vinyl acetate, vinyl alcohol, maleic acid, Maleic anhydride, acrylic acid, acrylic ester, methacrylic acid,
It is also possible to copolymerize at least one selected from methacrylic acid ester, acrylonitrile, vinylidene chloride, vinyl propionate, etc., and further modify the copolymer by saponification, sulfonation, phosphorylation, etc. You can also do it. Regarding these resins, please refer to Japanese Patent Application Laid-open No.
No. 7-44227, No. 60-235814, No. 60-
No. 238306, No. 61-243933, No. 62-9
It is described in publications such as No. 521.

(2) Polyurethane resin with polar groups introduced Polar groups are introduced into the side chains of polyurethane resin. Polyurethane resin is generally obtained by the reaction of a polyhydroxy compound and a polyisocyanate, but there is a method in which a compound having the above-mentioned polar groups is mixed as a raw material for the polyurethane resin, and a method in which the hydroxyl groups remaining at the terminal or side chain of Polyurekne+M resin is removed by the above-mentioned method. The above-mentioned polar group can be introduced into the polyurethane resin by a method of modifying the polyurethane resin with a compound having a polar group. The amount of polar groups introduced into the polyurethane resin is 0.01 to 1.0 mm ol/
g, preferably 0.1 to 0.5 mm o 17
It is g.

If the amount exceeds the upper limit, intermolecular or intramolecular aggregation occurs, which not only adversely affects dispersibility, but also causes selectivity to the solvent, resulting in the problem that ordinary general-purpose solvents cannot be used.

Polyurethane resins include aliphatic polyesters, aromatic polyesters, or mixtures thereof, and various polyurethane resins made by synthesizing polycaprolactone-based or polycarbonate-based polyols with a chain extender diisocyanate.The process of synthesizing these polyurethane resins dimethylolpropionic acid, trimellitic acid, 5
There are products in which the aforementioned polar groups are optionally introduced using -sodium sulfoisophthalic acid, 2-potassium sulfoterephthalic acid, etc. For these resins, please refer to Special Publication No. 5B-4
No. 1565, No. 61-18809, JP-A-59-14
It is described in publications such as No. 8127 and No. 62-40615.

The above polymers can be used alone or as a binder.
A mixture of more than one species is used. The weight average molecular weight is within the range of 20,000 to 80,000, more preferably within the range of 25,000 to so, ooo, and furthermore, low molecular weight ones with a molecular weight of 3,000 or less are 3% by weight or less,
More preferably, it is 2% by weight or less. Methods to obtain such a weight average molecular weight include adjusting the conditions such as the polymerization catalyst used when synthesizing these resins, or increasing the molecular weight of the resin itself, but the most effective method is to Once synthesized, the resin is precipitated with a poor solvent such as alcohols such as methanol, ethanol, and isopropanol, aromatics such as benzene, toluene, and xylene, or aliphatic hydrocarbons such as pentane, hexane, heptane, and octane. Fractional precipitation is a reliable method, and has the advantage that the compounds to be removed can be easily selected.

In addition to the characteristic binder of the present invention described above, a high molecular weight polymer that can be conventionally used as a binder can be used in combination without exceeding the proportion thereof. Examples of this polymer include acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, other acrylic acid copolymers, nylon-silicone resin, cellulose derivatives such as nitrocellulose, and vinylidene chloride-acrylonitrile. Copolymers, polyamide resins, polyvinyl butyral, styrene-butadiene copolymers, phenolic resins, epoxy resins, urea resins, melamine 414 resins, polyester resins, chlorovinylnythyl-acrylic ester copolymers, meccrylic ester copolymers Polymers, diisocyanate blend polymers, amino resins,
There are various types of synthetic rubber.

The present invention is further characterized in that a thermosetting polyisocyanate compound is added as a binder component in order to improve the durability of the magnetic layer. Examples of polyisocyanate compounds include tolylene diisocyanate, 4.
Isocyanates such as 4-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1.5-diisocyanate, o-)luidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate, and further these isocyanates and polyalcohols. and polyisocyanates produced by condensation of isocyanate 111. Commercial products of these various polyisocyanates include, for example, "Coronet) LJ,""CoronetHLJ,""Coronet) 2030 J,""Coronet) 2031 J,""Coronet) 2036 J,""Coronet) 3014 J,"
Coronate 2015 J, r Millione) MRJ, ``Millione) MTLJ, ``Dalt Sec 1350 r Dalt Motsuku 21fu 0 J, ``Dalt Sec 217 Or Dalt Sec 2280.

(All of the above are product names: Made by Nippon Polyurethane Industries)
, [Takenate D-102J, "Takenate D-11O
NJ, "Takene) D-200J, "Takene) D
-202J, C or above, manufactured by Takeda Pharmaceutical Co., Ltd.), r Dismodule L, Dismodule IL, Dismodule N, Dismodule HLJ (manufactured by Sumitomo Bayer ■), etc. Alternatively, two or more types can be used in combination by taking advantage of the difference in curing reactivity.

Further, for the purpose of accelerating curing, it is desirable to use a compound having a large number of functional groups such as hydroxyl groups and amino groups.

In addition to the binder component described above, it is also possible to further add a reinforcing agent for the magnetic layer, a lubricant, an antistatic agent, a dispersant, and the like.

Reinforcing agents include α-alumina, fused alumina, chromium oxide, corundum, α-iron oxide, silicon nitride, boron nitride,
There are powders of substances with a Mohs hardness of 6 or more, such as silicon carbide, molybdenum carbide, boron carbide, tungsten carbide, diatomaceous earth, and dolomite, with an average particle size of o, oos to 5IIm, which can be used singly or in combination of two or more as desired. used. These reinforcing agents range from 0.05 to 100 parts by weight of binder.
It is used in proportions within the range of 20 parts by weight.

Lubricants include silicone oil, graphite, molybdenum disulfide, boron nitride, graphite fluoride, tungsten disulfide,
These include fluorinated alcohols, polyolefins, polyglycols, alkyl phosphate esters, polyphenyl ethers, higher fatty acid esters, higher fatty acid amides, higher fatty acid alcohols, and antioxidants such as alkyl phenols, which are commonly used as additives in lubricating oils. Rust inhibitors such as naphthenic acid, oil agents such as lauryl alcohol, extreme pressure agents such as dibenzyl sulfide, other cleaning and dispersing agents, viscosity index improvers, pour point depressants, antifoaming agents, etc. can also be added. . These lubricants are used in proportions ranging from 0.05 to 20 parts by weight per 100 parts by weight of binder.

Antistatic agents include graphite, various carbon blacks, carbon black graft polymers, conductive powders such as tin oxide-antimony oxide compounds; natural surfactants such as saponin; alkylene oxides, glycerin, glycidol, and Various nonionic surfactants such as alcohols and polyhydric alcohol esters; higher alkyl amines, cyclic amines, hydantoin derivatives, amides, amines, ester amides, quaternary ammonium salts,
Various cationic surfactants such as pyridine, other heterocyclic compounds, phosphoniums or sulfoniums; various anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester groups, and phosphoric acid ester groups; Examples include various amphoteric surfactants such as amino acids, aminosulfonic acids, sulfuric acid esters or phosphoric acid esters of amino alcohols, and alkyl betaine. These antistatic agents may be used alone or in combination of two or more. The above-mentioned antistatic agent not only has the performance as an antistatic agent, but also has properties such as improved dispersibility, improved magnetic properties, improved lubricity, and improved applicability. The antistatic agent is approximately 0.01 to 10 per 100 parts by weight of the binder.
Used in proportions of parts by weight.

Dispersants include fatty acids having 10 to 22 carbon atoms, such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, lylunic acid, and stearolic acid; Examples include metal soaps made from fatty acids such as alkali metals, alkaline earth metals, copper, and lead, lecithin, higher alcohols, and sulfuric acid esters and phosphoric acid esters of these alcohols. °These dispersants may be used alone or in combination of two or more. The above dispersants are used in amounts ranging from about 0.01 to 10 parts by weight per 100 parts by weight of binder.

The coating solution for forming a magnetic layer is basically prepared by mixing the above components, that is, by dissolving the desired binder in a solvent that can dissolve the selected binder, and adding fine ferromagnetic powder to the solution. It is prepared by adding, stirring, and uniformly dispersing. Examples of solvents for preparing the binder solution for IA include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and isophorone, methanol, ethanol, propatool, butanol, isopropyl alcohol, isobutyl alcohol, and methylhexanol. Alcohol solvent, methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate,
Ester solvents such as isopropyl acetate, ethyl butyrate, ethyl lactate, ethylene glycol monoacetate, ether solvents such as glycol acetate monoethyl ether, glycol dimethyl ether, glycol monoethyl ether, tetrahydrofuran, dioxane, benzene,
Aromatic hydrocarbon solvents such as toluene, xylene, cresol, styrene, halogenated hydrocarbon solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, dichlorobenzene, N,N-dimethylformamide, etc. There are several types of solvents, which can be appropriately selected depending on the selected polymeric substance, or two or more types can be used in combination.

These organic solvents are selected so as to be able to completely dissolve the components to be dissolved, and in the case of a mixed solvent, the selection of the solvent and the respective quantitative ratios are determined as appropriate. Furthermore, these solvents must not deteriorate the properties of the ferromagnetic fine powder, which is the main component of the magnetic layer.

For dissolving and dispersing various components in organic solvents, examples are two-roll mill, three-roll mill, ball mill, pebble mill, thoron mill, sand grinder, attritor, high-speed impeller, dispersion machine, high-speed sootone mill, high-speed impact mill, disper, and Nigu. , high speed mixer, ribbon blender, coney goo, intensive mixer, tumbler
, blender, disperser, homogenizer, ultrasonic disperser, etc. are used.

The magnetic layer forming coating liquid after dispersion treatment is coated with air doctor coat, blade coat, air knife coat, etc.
squeeze coat, impregnation coat, reverse roll coat,
It is applied onto a support using various coating methods such as transfer roll coating, gravure coating, cast coating, and spray coating. The coating amount is 2μ in dry thickness.
m or less.

Non-magnetic supports forming the magnetic layer include, for example, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyolefin resins such as polypropylene, cellulose derivatives such as cellulose diphroate and cellulose triacetate, and vinyl chloride resins such as polyvinyl chloride. , film-like bodies or sheet-like bodies of plastics such as polysulfone resin, polycarbonate resin, polyimide resin, and boria resin, or foil-like bodies of metal materials such as aluminum and copper, or various ceramic materials;
There are plate-like bodies. The shapes of these supports may be pre-formed, or they may be formed by, for example, cutting after forming a magnetic layer or a back layer (to be described later). Various pretreatments such as treatment, undercoat treatment, heat treatment, metal vapor deposition treatment, and alkali treatment may be performed.

The magnetic layer coated on the support by the various methods described above is usually subjected to a magnetic field orientation treatment during drying to orient the ferromagnetic particles within the magnetic layer, and then drying is completed.

Techniques for applying these coating liquids for forming a magnetic layer, magnetic field alignment treatment, drying, and the like are conventionally known, and can be used or applied appropriately for the present invention.

In addition, in the case of a coated product, especially a tape-shaped body (I tape) using a plastic film as a support, it is desirable that a back layer with a desired composition be formed on the back side of the coated product. Ingredients include the binders and compounds exemplified and detailed as components of the magnetic layer forming coating solution.
There are IA solvents and inorganic lubricants, and they can be appropriately selected and configured. The inorganic lubricant is a fine powder with an average particle size of 0.8 μm or less, particularly preferably 0.4 μm or less.

The mixing ratio of the binder and the inorganic lubricant in the back layer is within the range of 1j0.1 to 1:4 (weight ratio). Then, as in the case of forming the magnetic layer, fine powder of an inorganic substance as a lubricant is uniformly dispersed in an organic solvent as a binder to prepare a coating liquid for forming a back layer. This coating solution is then applied to the back side of the support on which the magnetic layer is or should be formed, and dried to form a back layer. The coating layer in the magnetic recording medium should be made as thin as possible in order to increase the recording rate of 8 degrees per unit of the magnetic recording medium, and therefore the thickness of the back layer is preferably about 0.3 to 1.5 pni. The preparation, coating, drying, etc. of the coating liquid for forming the back layer are the same as those for the magnetic layer. At this time, the practitioner may decide as appropriate whether to provide the magnetic layer or the back layer on the support first.

The magnetic layer and back layer coated as described above are subjected to various surface treatments such as calender treatment as desired, and depending on the form of the support, the coated material is coated in the desired form, for example, in the form of a tape, etc.
Cut into shapes such as cards, discs, and sheets, and then store them in various cassettes or storage cases depending on the type of magnetic recording medium, or attach them to a base or laminate them with other materials. Make it a concrete product. In either case, those skilled in the art can easily manufacture the magnetic recording medium of the present invention by using or applying conventional techniques and turn it into a desired product.

(Example) Hereinafter, the present invention will be explained in detail and concretely based on Examples and Comparative Examples.The measurement results of the sample on each side will be summarized and explained at the end. All "parts" in the compounding ratios in the examples are "parts by weight."

Susei Group-1 A coating solution for forming a magnetic layer prepared as below was applied to one side of a polyethylene terephthalate film with a thickness of 10 am as a support, and after performing a magnetic field orientation treatment using a cobalt magnet, a temperature of 100' was applied. It was dried in an atmosphere of C for 1 minute to form a magnetic layer with a thickness of 3 μm.

° / 2! 1 Composition: Ferromagnetic alloy fine powder (Smtt! 50M/mg, coercive force Hc: 1.5000e) -------
100 copies "Resin B' listed in Table 1...
・・・・・・Resin H1−・・described in Part 10, Table 1
−・・−・−・−・・・10 parts carbon black・・・
−−−−−−−・−・・−・−・・−・・・・・・・
・−・・1 part chromium oxide powder・・・・・・・−・
・−・−・・・・・・−・−・−・・−Two parts stearic acid ・・−−−−−・・−・・−・−・・−・・
・・・・・・・・・−・・・−Two-part stearin, amyl acid
・・−・・−・−・−・・−・−・・・・・−・・・ 2
Methyl ethyl ketone・・・・・・・−・−・・・−・
・・−・・−・・150 parts cyclohexanone・−・−・
Preparation of 150 parts: The above composition was placed in a sand grinder together with glass peas, mixed for 2 hours, and then subjected to dispersion treatment. A 7.5% by weight ethyl acetate solution of a trifunctional polyisocyanate compound prepared by an addition reaction of toluene diisocyanate and 1 mol of trimethylolpropane, 5 parts of Dismodur LJ (manufactured by Bayer AG, West Germany) was added to a methyl ethyl ketone/toluene mixture. Add 10 parts of the solution and mix by stirring at high speed to create a "magnetic layer forming coating solution."
was prepared.

After forming the magnetic layer as described above, it was subjected to calender treatment and thermosetting treatment, and further cut into a tape shape with a diameter of 8 mm to prepare a magnetic recording tape.

One sample is 1 m long.

2 to 7, ' 1 and 2 □ Carry out in the same manner as in Example 1 except that resins shown in Table 1 were used in each case instead of resin B and resin H in Example 1, Created magnetic recording tape. These are "sample 2~7m" and "comparative sample l~" respectively.
21.

Resin A: Polyester polyurethane resin containing 6 x 10-' equivalents/g of SOs Na groups.

(Synthesized based on the example described in Japanese Patent Publication No. 58-41565.) ■Resin B: Methyl ethyl ketone/toluene of resin A: l
1 kg of a 30% by weight solution of 1/1 was precipitated in 6 kg of hexane and dried.

■Resin C: Methyl ethyl ketone/tolu X7:1 with resin
1 kg of 30% by weight solution of /1 in hexane/toluene = 7
/3.6 kg and dried.

■Resin D: Polyester polyurethane resin containing 6×10-' equivalents/g of C0OH groups.

(Synthesized based on the example described in JP-A-59-148127.) ■Resin E: Resin methyl ethyl ketone/toluene = 1
1 kg of a 30% by weight solution of /l was precipitated in 6 kg of hexane and dried.

■Resin F: Resin methyl ethyl ketone/toluene: 1
1 kg of a 30% by weight solution of 71 was precipitated in hexane/toluenia/3.6 kg and dried.

■Resin G: SOs Na group 6X10-' equivalent/g
A vinyl chloride copolymer containing

(Example 1 described in JP-A-60-238306)
Synthesized based on. ) Resin H: 1 kg of a 30% by weight solution of Resin G in methyl ethyl ketone was precipitated in 10 kg of methanol and dried.

(2) Resin I: 1 kg of a 30% by weight solution of Resin G in methyl ethyl ketone was precipitated in 6 kg of methanol and dried.

6mllJ: Coo) i group! 6x10-'111/
gt-containing vinyl chloride copolymer rMPR-T, M”
(8 Shin Kagaku■!KW) ■Resin: 1 kg of a 30% by weight solution of Resin J in methyl ethyl ketone was precipitated in 10 kg of methanol and dried.

(2) Resin L: 1 kg of a 30% by weight solution of Resin J in methyl ethyl ketone was precipitated in 6 kg of methanol and dried.

(Hereinafter, blank space) Table 1 and above 7 About each sample created ■Video S/N
, ■ Video S/N decrease after repeated 3o pass driving, ■
After repeatedly running each sample for 30 passes, the dirt on the video head and the dirt on the audio head (2) were also measured, and the results shown in Table 1 were obtained. In addition, each measurement method is as follows.

1 Ri 1 selection ■ Video, S/N: Each sample was recorded using a videotape recorder rFUJ lX-8J (Product name: Fuji Photo Film ■
Noise Meter R925R"
(manufactured by product name Nijiback ■) to reduce the comparative sample 1 to OdB
", and the difference in S/H of each sample was determined.

(2) Decrease in video S/N after repeatedly running the bus for 30 passes: Based on the initial video S/N of each sample, the decrease in video S/N after running each sample repeatedly for 30 passes is shown.

■ and ■: Head dirt: Video head (■) and audio head (after running each sample repeatedly for 30 passes)
■) Observe the stains under a microscope, and select those with no stains.
1 or less The more soiled the skin, the more it is marked with O5Δ and ×.

Table 1 Note: In the table, () indicates the content of molecular tilt 3.000 or less is 3% by weight or more.

As is clear from the results shown in Table 1, it can be seen how the durability of the magnetic recording medium deteriorates when a low molecular weight resin is used as a binder component in the magnetic layer. It is clear that increasing the content of high molecular weight components is extremely effective in improving the durability of the magnetic layer.

〔Effect of the invention〕

According to the present invention, the low molecular weight component of the resin in the binder for forming the magnetic layer is reduced to a very small amount to provide magnetic recording that has excellent magnetic properties and high running durability, and has low running friction and video S/N degradation. Since the present invention can provide a medium, the present invention is well known in the art. Display of the case 1985 Patent Application No. 97524 2, Title of the invention! ! Magnetic recording media, person making the amendment Relationship to the case: Patent applicant name: (520) Fuji Photo Film Co., Ltd. 4, agent address: 29th floor, Kasumigaseki Pill, 3-2-5 KasumigaoQ, Chiyoda-ku, Tokyo 100 6. Subject of amendment: Column 7 of "Detailed Description of the Invention" of the specification. Contents of amendment: The column of "Detailed Description of the Invention" of the specification is amended as follows.

(1) "Propynyl group" on page 12, line 12 of Akira 11n is corrected to "propenyl group."

(2) r in the 14th member of the same book, lines 3 to 4 (
CH2CH)L (Y)r-(CH20H)nCI
X J (3) Douma, page 14, line 4 from the bottom to page 15, line 1
In line 1, "It is better to do something that is related to solubility." ] and correct it.

(4) “0.01 to 1.
011101/(l J [0,001~0.5110
Correct it to 1 J.

(5) [0,1-0.5 on page 16, line 14 of the same store
111101/Q J to "0.01 to 0.5 mol
Correct it with J.

(6) Correct "kakete" in page 35, line 9 of Mukai to "kake".

Claims (4)

[Claims] (1) In a magnetic recording medium in which a magnetic layer in which fine ferromagnetic powder is uniformly dispersed in a binder is provided on a nonmagnetic support, the binder has a weight average molecular weight of 20,000 to 20,000.
80,000, and the weight average molecular weight of 3,000 or less is 3% by weight or less, and the magnetic recording medium is at least one selected from the group consisting of vinyl chloride resins and urethane resins. . (2) The magnetic recording according to claim 1, wherein the ferromagnetic material is a ferromagnetic alloy whose specific surface area (S_B_E_T) measured by the BET method is 40 m^2/g or more. Medium. (3) The binder is -SO_3M, -OSO_3M, -C
OOM, -OPO(OM_1)(OM_2), -PO(
OM_1) (OM_2), [M, M in each of the above substituents
_1 and M_2 are hydrogen atoms, alkali metal atoms, or -NR_1R_2R_3R_4 (R_1, R_2, R_
3 and R_4 represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group, a substituted alkyl group, or a substituted alkenyl group. ) represents. ] from 1 to 50 x 10^-^
The magnetic recording medium according to claim 1, characterized in that the magnetic recording medium contains 6 equivalents/g. (4) The magnetic recording medium according to claim 1, further comprising a polyisocyanate compound as a binder component in addition to the binder.